Static dissipative textile and method producing the same

ABSTRACT

The present invention relates generally to a static dissipative textile having an electrically conductive surface achieved by coating the textile with an electrically conductive coating in a variety of patterns. The electrically conductive coating is comprised of a conducting agent and a binding agent, and optionally a dispersing agent and/or a thickening agent. The static dissipative textile generally comprises a fabric which may be screen printed or otherwise coated with a conductive coating on the backside of the fabric so that the conductive coating does not interfere with the appearance of the face of the fabric. The economically produced fabric exhibits relatively permanent static dissipation properties and conducts electric charge at virtually any humidity, while the conductive coating does not detrimentally affect the overall appearance or tactile properties of the fabric. Also encompassed within this invention is a method for producing a static dissipative textile having an electrically conductive surface.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/244,934, filed on Sep. 16, 2002 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to a static dissipative textilehaving an electrically conductive surface which is achieved by coatingthe textile with an electrically conductive coating in a wide variety ofpatterns. The electrically conductive coating is generally comprised ofa conducting agent and a binding agent, and optionally a dispersingagent and/or a thickening agent. The static dissipative textilegenerally comprises a fabric which may be screen printed or otherwisecoated with an electrically conductive coating on the backside of thefabric so that the conductive coating does not interfere with theappearance of the face of the fabric. The economically produced fabricexhibits relatively permanent static dissipation properties and conductselectric charge at virtually any humidity, while the conductive coatingdoes not detrimentally affect the overall appearance or tactileproperties of the fabric. The fabric may be ideal for use in suchend-use products as automotive upholstery; commercial and residentialupholstery; cleanroom garments, wipes, and mops; napery; and apparel.Also encompassed within this invention is a method for producing astatic dissipative textile having an electrically conductive surface.

It is generally known that some textile fabrics have inherent staticgeneration problems, particularly synthetic fabrics such as polyester ornylon, and particularly in low humidity environments. Static generationoccurs typically when two objects are brought into contact with eachother and then separated. Generation is usually exacerbated when theobjects are rubbed against each other, such as, for example, when twofabrics are rubbed against each other, resulting in a charge transferbetween the two objects. This resulting potential difference between theobject incurring the charge transfer and the surrounding environment,which may be tens of thousands of volts, can lead to uncomfortable anddangerous electric shocks. Static shocks can also result in damage tosensitive electronic components such as computer chips and sensorsmanufactured, for example, in cleanroom environments. Since one of theobjects may be a fabric, the need exists for static dissipative fabricsto eliminate or reduce static electric charge created when an object isseparated from a fabric.

One method of reducing the static charge on a fabric is to treat thefabric with a topical anti-static agent. These agents, which arecommercially available, are typically quaternary ammonium salts, orionic solutions containing small ions such as lithium ions. This type ofanti-static treatment for fabric is disclosed, for example, in U.S. Pat.No. 5,643,865 to Mermelstein et al., U.S. Pat. No. 5,622,925 to deBuzzaccarini et al., and U.S. Pat. No. 5,254,268 to Schwartz. Othertopical agents reduce static shock by lubricating the surface of thefabric with a hand modifier or softening agent thereby decreasing thefriction between the fabric and the object rubbed against it. Both ofthese approaches suffer from a lack of durability to repeating abrasion.The softening agents and conducting finishes are partially removedduring each abrasion or rubbing event; thus, the treatment is notpermanent. Also, the fabric may develop issues with crocking. Inaddition, the conducting mechanism of the topical treatments depends onthe presence of a small amount of water. Therefore, their effectivenessis quite limited in low humidity environments such as those encounteredduring winter months.

A method of producing a relatively permanent anti-static fabric thatperforms at substantially all humidity levels is to provide electricalconductivity to the fabric by the incorporation of conductive yarns intothe fabric during the fabric formation process. The number and frequencyof the conductive yarns, as well as their proximity to the surface ofthe fabric generally determine the amount of conductivity, andultimately the amount of static protection provided by a particularfabric. In order to increase the effectiveness of static dissipation,the conducting yarns should intersect each other, thus forming aconductive grid. This method is used in many end-use applications suchas in cleanroom garments and anti-static wipes. This method isdisclosed, for example, in U.S. Pat. Nos. 4,557,968 and 4,606,968 bothto Thornton et al. However, this method is limited by the high cost ofconductive yarns and the cost of weaving, knitting, or stitching fabricswith these conductive yarns. Additionally, these conductive yarns areusually colored such that they may be undesirably visible on the face ofthe fabric. Furthermore, an end-use determination for a fabric must bemade in advance of the fabric formation process so that the conductiveyarns may be incorporated into the fabric at the onset of fabricformation.

Still another method of producing anti-static fabrics is to treat theentire surface of the fabric with a conductive paste or coating. Thiscoating can be in the form of an intrinsically conducting polymer, suchas that disclosed in U.S. Pat. No. 4,803,096 to Kuhn et al., or in theform of a conductive particle dispersed in a non-conducting matrix suchas that described in U.S. Pat. No. 5,804,291 to Fraser. Although thesemethods overcome the limitations of topical treatments and are generallyless expensive than incorporation of conductive yarns, they suffer fromthe fact that conductive coatings are normally highly colored and areoften visible on the face of the fabric when used over the entiresurface of the fabric. Also, the hand (or feel), drape, and air porosityof the fabric can be influenced adversely by impregnating the entiresurface of the fabric with a matrix containing conductive particles.

Other methods have been disclosed in which an entire substrate is coatedwith a conductive polymer and then selected portions of the conductivepolymer are removed. For example, U.S. Pat. No. 5,624,736 to DeAngeliset al. teaches a method in which a substrate is coated with a conductivepolymer across its entire surface. The fabric is then coated in selectareas with a protective film. The substrate is then subjected to a thirdtreatment in which a chemical etching agent is used to remove theconductive polymer from the exposed portions of the substrate which werenot covered with the protective film. Finally, the substrate is rinsedto remove the excess etching agent. Such a process, with so manyoperational steps, is rather complicated and lengthy and, like anyprocess which involves coating an entire substrate only to remove largeportions of the coating, necessarily involves a good deal of materialloss. Also, this method leaves an insulating coating over the conductingareas, thus reducing the effectiveness of static dissipation. Thismethod further suffers from the lack of breathability imparted to theconductive areas by the protective film. Another example of patternedconducting textile materials is disclosed in U.S. Pat. No. 6,001,749 toChild et al. This patent teaches a method in which areas of a fabric arecoated with a repellant finish that inhibits the deposition of aconductive coating. The fabric is then coated with a conductive polymerleaving the pre-treated areas substantially free from the conductivepolymer. This method leaves the highly colored conductor on the face andback of the fabric, thus detrimentally affecting the appearance, hand,and/or permeability of the fabric. Accordingly, both U.S. Pat. Nos.6,001,749 and 5,624,736 are generally more suited to applications inElectromagnetic Interference Shielding (EMI).

Thus, a need exists for an economically manufactured fabric withrelatively permanent anti-static properties that are inherent atvirtually any humidity and does not affect the overall appearance ortactile properties of the fabric.

SUMMARY OF THE INVENTION

In light of the foregoing discussion, it is one object of the currentinvention to achieve a static dissipative textile having an electricallyconductive surface. The static dissipative textile is generallycomprised of a fabric. The electrically conductive surface may beachieved by screen printing the fabric with an electrically conductivecoating, wherein the conductive coating includes a conducting agent anda binding agent, and optionally a dispersing agent and/or a thickeningagent. The fabric may be coated in any pattern which achieves thedesired static dissipative property for the fabric's end-use. The fabricmay be coated on one or both sides of the fabric as determined generallyby the end-use of the fabric by considering the desired appearance ofthe coated fabric and/or the conductive performance of the coatedfabric. The resulting electrically conductive fabric may be suitable inend-use applications such as automotive upholstery and other automotiveinterior fabrics, such as door panels, armrests, headrests, etc.;commercial and/or residential upholstery; cleanroom garments, wipesand/or other cleanroom accessories such as mops; napery; and apparel.

Another object of the current invention is to achieve a compositematerial, wherein the static dissipative textile may further comprise atleast one layer of a second fabric disposed adjacent to the electricallyconductive coating. The second fabric may be woven, knitted, or nonwovenfabric. Alternatively, the static dissipative textile may furthercomprise at least one layer of foam material disposed adjacent to theelectrically conductive coating. The composite material may furtherinclude one or more layers of woven, knitted, or nonwoven fabric; one ormore layers of film; one or more layers of adhesive; or combinationsthereof. The composite material may be used, for example, in automobileinteriors, such as in automotive upholstery, wherein the upholsteryfabric is typically adhered to a foam backing through the use ofadhesive, heat lamination, or the like. The composite material may beapplicable for use in other areas such as, for example, in residentialor commercial upholstery or in carpeting.

It is also an object of the current invention to achieve a method forproducing a static dissipative textile having an electrically conductivesurface. The method generally comprises the steps of providing aknitted, woven, or nonwoven fabric, coating one or both sides of thefabric with an electrically conductive coating in a pattern comprised oflines, and drying the fabric. The fabric may then be exposed to one ormore mechanical and/or chemical textile finishing processes known tothose skilled in the art.

Other objects, advantages, and features of the current invention willoccur to those skilled in the art. Thus, while the invention will bedescribed and disclosed in connection with certain preferred embodimentsand procedures, such embodiments and procedures are not intended tolimit the scope of the current invention. Rather, it is intended thatall such alternative embodiments, procedures, and modifications areincluded within the scope and spirit of the disclosed invention and arelimited only by the appended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts one embodiment for the static dissipative textile of thepresent invention. The pattern shown is a diagonal grid of intersectinglines which have a line spacing of about 1 inch and a line width ofabout 2 millimeters. The coating coverage is about 15%.

FIG. 2 depicts another embodiment for the static dissipative textile ofthe present invention. The pattern shown is a diagonal grid ofintersecting lines which have a line spacing of about 0.5 inches and aline width of about 2 millimeters. The coating coverage is about 29%.

FIG. 3 depicts a further embodiment for the static dissipative textileof the present invention. The pattern shown is a diagonal grid ofintersecting lines which have a line spacing of about 0.5 inches and aline width of about 1 millimeter. The coating coverage is about 15%.

FIG. 4 depicts yet another embodiment for the static dissipative textileof the present invention. The pattern shown is a series of repeatingwords which are connected to one another.

FIG. 5 is a graph depicting the percolation thresholds for both graphitewhiskers and graphite spheres shown as surface resistance of the fabricversus percent volume of graphite.

FIG. 6 is a bar graph depicting the effect of line spacing and linewidth on static performance shown as triboelectric charge versus linespacing and line width.

FIG. 7 is a bar graph depicting fabric durability against bounce shownas triboelectric charge versus three types of fabric—a control (noconductive particles present), a static dissipative fabric of thepresent invention having an acrylic binder, and a static dissipativefabric of the present invention having a urethane binder.

FIG. 8 is a schematic drawing of the static testing machine used toperform the Static Test on the fabric of the present invention. It isdisplayed in a setup configuration prior to performing the testprocedure.

FIG. 9 is a schematic drawing of the static testing machine used toperform the Static Test on the fabric of the present invention. It isdisplayed in a setup configuration after the test has been performed.

DETAILED DESCRIPTION OF THE INVENTION

A static dissipative textile is provided which has relatively permanentanti-static properties which are achieved at substantially all relativehumidities without significantly compromising the textile hand (or feel)of the textile or the surface appearance of the textile. The staticdissipative textile generally comprises a fabric coated on at least onside with a pattern of an electrically conductive coating.

The fabric of the current invention can be formed from fibers such assynthetic fibers, natural fibers, or combinations thereof. Syntheticfibers include, for example, polyester, acrylic, polyamide, polyolefin,polyaramid, polyurethane, regenerated cellulose, and blends thereof.More specifically, polyester includes, for example, polyethyleneterephthalate, polytriphenylene terephthalate, polybutyleneterephthalate, polylatic acid, and combinations thereof. Polyamideincludes, for example, nylon 6, nylon 6,6, and combinations thereof.Polyolefin includes, for example, polypropylene, polyethylene, andcombinations thereof. Polyaramid includes, for example,poly-p-phenyleneteraphthalamid (i.e., Kevlar®),poly-m-phenyleneteraphthalamid (i.e., Nomex®), and combinations thereof.Natural fibers include, for example, wool, cotton, flax, and blendsthereof.

The fabric can be formed from fibers or yarns of any size, includingmicrodenier fibers and yarns (fibers or yarns having less than onedenier per filament). Furthermore, the fabric may be partially or whollycomprised of multi-component or bi-component fibers or yarns which maybe splittable along their length by chemical or mechanical action. Thefabric may be comprised of fibers such as staple fiber, filament fiber,spun fiber, or combinations thereof.

The fabric of the current invention may be of any variety, including butnot limited to, woven fabric, knitted fabric, nonwoven fabric, orcombinations thereof. They may optionally be colored by a variety ofdyeing techniques, such as high temperature jet dyeing with dispersedyes, thermosol dyeing, pad dyeing, transfer printing, screen printing,or. any other technique that is common in the art for comparable,equivalent, traditional textile products. If yarns or fibers are treatedby the process of the current invention, they may be dyed by suitablemethods prior to fabric formation, such as, for instance, by packagedyeing or solution dyeing, or after fabric formation as described above,or they may be left undyed.

The electrically conductive coating may be disposed on the fabric in anypattern. The pattern is typically comprised of a plurality of lines. Asused herein, a line is defined as a continuous conductive path.Generally, this continuous conductive path is characterized by aconductivity equal to or less than 10¹³ ohms per inch. The lines of thepattern may be substantially straight lines, curved lines, orcombinations thereof. The lines may form at least one intersection, andthey may form a plurality of intersections. As used herein, anintersection is defined as one point having at least 3 lines radiatingfrom it. The lines of the pattern of the electrically conductive coatingtypically define an opening not greater than about 3 inches square, andpreferably not greater than about 2 inches square. “About three inchessquare” typically represents a square area with approximately threeinches on each side, and “about two inches square” typically representsa square area with approximately two inches on each side. For example,when a three inch square is placed on a fabric having an electricallyconductive coating, it should make contact with the electricallyconductive coating in at least one location. However, it is foreseeablein some instances that the edges of the fabric may have areas free fromthe electrically conductive coating greater than about 3 inches square.One embodiment includes a pattern comprised of a series of lines whichintersect each other to form a grid pattern. The grid pattern may bediagonal. As shown, for example, in FIGS. 1 through 3, the staticdissipative textile 100 displays an electrically conductive coating 200disposed on the fabric 300 in a diagonal grid pattern 400 having one ormore intersections 410. In another embodiment, such as the one shown inFIG. 4, the static dissipative textile 100 displays an electricallyconductive coating 200 disposed on the fabric 300 in a pattern ofconnected letters or words 500 with one or more intersections 510.Additionally, a pattern may be comprised of lines which form otherconnecting patterns or designs such as, for example, lightning bolts.For patterns having one or more intersections as shown in FIGS. 1through 4, a cut or break in the lines of the electrically conductivecoating generally will not eliminate the static dissipative property ofthe textile. The electrically conductive coating may be applied to theface of the fabric, the back of the fabric, or both the face and back ofthe fabric.

The electrically conductive coating generally includes a conductingagent and a binding agent. The electrically conductive coating may alsooptionally include a dispersing agent and/or a thickening agent.

One potentially preferred, non-limiting conducting agent is graphite,such as, for example, Timrex® SFG available from Timcal Ltd. ofSwitzerland. Other conducting agents include, for example, Zelec®(available from Milliken Chemical of Spartanburg, S.C.); carbonparticles; intrinsically conductive polymers; metal; metal oxides; metalshavings; fibers or beads coated with graphite, carbon particles,intrinsically conductive polymers, metal, metal oxides, or metalshavings; and the like; and combinations thereof. The conducting agentmay be comprised of particles of various shapes, such as spheres, rods,flakes, and the like, and combinations thereof. The conducting agent maybe comprised of conducting particles having a size between about 0.1 andabout 100 microns, or more preferably having a size between about 1 andabout 5 microns. Conducting agents may be characterized by having anaspect ratio number which is the ratio of a conducting particle's lengthdivided by its width. For example, a perfect sphere has an aspect ratioof one. The longer the particle (i.e., the more rod-like the particle),the higher the aspect ratio. Generally, for a conducting agent having ahigh aspect ratio, less conducting agent is needed to provide the sameelectrical conductivity in an object, such as the present invention,when compared to a conducting agent made of a similar conducting agentbut having a lower aspect ratio. It is generally preferable that theaspect ratio of the conductive particle of the present invention isequal to or greater than about 2. It may be more preferable that theaspect ratio be equal to or greater than about 3, and even morepreferable that the aspect ratio be equal to or greater than about 4.

The binding agent included in the conductive coating of the presentinvention typically provides a non-conducting matrix which holds theconducting particles together and helps them bond to the fabric. Bindingagents include water-borne latexes, solvent-borne polymer systems,liquid rubbers, thermoplastic hot melts, thermoset hot melts,multi-component reactive polymers, and the like, and combinationsthereof. More specifically, binding agents may be acrylic latex,polyurethane, silicone, polyvinyl chloride latex, and the like, orcombinations thereof. Binders generally vary, for example, in elongationand flex modulus properties which may affect the hand, drape, andstretch properties of the coated fabric. Thus, the selection of aparticular binder for the conductive coating of the present inventionmay depend on the end-use application of the static dissipative textile.It may be preferable that the binding agent has an elongation at breakequal to or greater than about 80 percent of the elongation at break ofthe fabric. Generally, the elongation at break of the fabric may becalculated in the direction of the fabric having the lowest elongationat break. It may be preferable that the binding agent has a glasstransition temperature equal to or less than about 0 degrees C. and amelting temperature equal to or greater than about 100 C.

It is generally known to those skilled in the art of the presentinvention that conductivity and resistance are inversely related to eachother and that a relationship exists between resistance and the amountof conducting agent present in an object. Generally, when conductivityis achieved by loading an insulating matrix with conductive particles,the conductive particles must be in contact with each other to provide apathway for the transport of electrical current. This is typicallyreferred to as percolation. The minimum amount of conductive particlesneeded to create at least one continuous pathway of particles contactingeach other though the material is referred to as the percolationthreshold. Below the percolation threshold, where no conductive pathwaysexist, the conductivity of the material is quite low and is related tothe resistance of the matrix material. When the loading of conductiveparticles is increased to the percolation threshold, a significant jumpin conductivity is generally observed. Further increases in theconductive particle loading will result in less dramatic increases inconductivity of the composite. This phenomenon of percolation isexplained in great detail in several texts including “Introduction toPercolation Theory” by Stauffer and Anarony (1992 Taylor and Francis,London). The aspect ratio of the conducting particle affects thepercolation threshold such that the higher the aspect ratio, the lowerthe percolation threshold. Thus, a conducting agent with a higher aspectratio will typically result in the need for less conducting agent to bepresent in an object (i.e., less raw material) to achieve the sameresistance than a conductive agent of similar composition with a loweraspect ratio. As a result, in choosing a conducting agent, the aspectratio and percolation threshold of the conducting agent may be evaluatedin determining which conducting agent will be best suited for aparticular end-use. In general, the strength of a matrix will decreasewith increasing loading of conductive agents. Therefore, it is generallypreferable to provide an electrically conductive coating with a loweramount of conducting agent by utilizing a conductive agent with a highaspect ratio. One embodiment utilizes a conducting agent wherein theconducting agent comprises less than about 30 volume percent of theelectrically conductive coating. In this instance, the conducting agentmay be graphite; carbon particles; intrinsically conductive polymers;metal oxides; fibers or beads coated with graphite, carbon,intrinsically conductive polymers, metal oxides; and combinationsthereof. In another example, one potentially preferred non-limitingembodiment of the present invention includes a graphite conductingagent, Timrex® SFG 15 available from Timcal Ltd. of Switzerland, with anaspect ratio of about 4 and a percolation threshold achieved at about 15volume percent of graphite in the electrically conductive coating.

The addition of a dispersing agent to the electrically conductivecoating is generally optional and may be desirable to assist in thedispersion of the conducting agent into the conductive coating. Thedegree of dispersion may affect the percolation threshold andconductivity. Many conducting particles, such as carbon black andgraphite, generally require dispersing agents in order to preventagglomeration in water. Agglomerated conducting particles typically willeffectively lower the aspect ratio of the material and increase thepercolation threshold. Dispersing agents can be non-ionic, anionic, orcationic in nature. The addition of a dispersing agent may not benecessary for conductive coatings that are not water-based. Furthermore,dispersing agents may not be necessary for use with conductive particlesthat are coated to facilitate dispersion or that disperse well in water.One potentially preferred, non-limiting embodiment utilizes a non-ionicsurfactant as the dispersing agent. Dispersing agents are commerciallyavailable, such as, for example, Syniube® 6277A available from MillikenChemical of Spartanburg, S.C.

The addition of a thickening agent to the conductive coating isgenerally optional and may be desirable to assist in the application ofthe coating to the fabric. The addition of a thickener generallyprovides control over viscosity and strike through to the uncoated sideof the fabric (for instance, when only one side of the fabric is coatedwith the conductive coating), and the resolution of the pattern can bepreserved. One potentially preferred, non-limiting embodimentincorporates an associative thickener such as a water-soluble acrylicpolymer as a thickening agent. A commercially available example of anassociative thickener is WTI Concentrate available from ABCO Industries,Incorporated of Roebuck, S.C. In another embodiment, the thickeningagent consists of a cellulosic thickener such as Natrosol®, manufacturedby Hercules Incorporated of Wilmington, Del.

Other additional chemicals may be added to the electrically conductivecoating before the coating is applied to the fabric. For example, theconductive coating may include a dye or pigment so that the color of thecoating matches the color of the fabric. Other additional chemicals maybe added, such as, for example, those typically used for abrasionresistance, fade resistance, flame resistance, and the like, andcombinations thereof.

One potentially preferred, non-limiting method for applying theconductive coating to the fabric is to apply the coating as a paste ontothe fabric through screen printing. Screen printing techniques have beenavailable for many years as a way of selectively producing a pattern ona fabric by forcing a paste through holes in a screen. For example, U.S.Pat. No. 4,365,551 to Horton; U.S. Pat. No. 4,854,230 to Niki et al.;U.S. Pat. No. 5,168,805 to Kasanami et al.; U.S. Pat. No. 5,493,969 toTakahashi et al.; and U.S. Pat. No. 6,237,490 to Takahashi et al. eachdescribe various screen printing methods and apparatus, and are hereinincorporated by reference. For purposes of the present invention, aconductive paste may be forced through a specially prepared screen ontoa substrate such as a fabric. The screen typically has areas in whichthe mesh has been blocked. These areas, which remain impervious to theconductive paste, correspond to patterned areas on the fabric in whichno conductive coating is desired. Other methods for printing substrates,such as transfer printing, lithographic printing, ink jet printing,digital printing, and the like, may also be used for applying theconductive coating to the fabric.

Prior to the coating process, the fabric may be dyed or undyed. If adyed fabric is desired, dyeing may be accomplished by any techniqueknown to those skilled in the art, such as, for example, by solutiondyeing the fiber used to make the fabric, dyeing the formed fabric in ajet dye machine, dyeing the formed fabric using a continuous processdyeing range, or any combination thereof. Additionally, the fabric mayalso be subjected to various face-finishing processes prior to screenprinting. For example, commonly assigned U.S. Pat. Nos. 5,822,835;4,918,795; and 4,837,902; incorporated herein by reference, disclose aface-finishing process wherein low-pressure streams of gas are directedat high velocity to the surface of a fabric. The process ultimatelysoftens and conditions the fabric due to vibration caused from airflowon the fabric.

Generally, the fabric of the present invention requires no pre-treatmentprior to the coating process. However, in one embodiment, apre-treatment process may be employed in order to assist in preventingthe electrically conductive coating from penetrating through to the faceside of the fabric. The pre-treatment process involves treating thefabric first with a cationic water-soluble polymer, such as Nalkat 62010from Ondeo Nalco Company of Franklin, Pa., prior to applying the coatingto the fabric. Treatment may be accomplished by immersion coating,padding, spraying, foam coating, or by any other technique whereby onecan apply a controlled amount of a liquid suspension to an article. Thefabric may optionally be dried before the conductive coating is applied.Drying can be accomplished by any technique typically used inmanufacturing operations, such as dry heat from a tenter frame,microwave energy, infrared heating, steam, superheated steam,autoclaving, or the like, or any combination thereof. When pre-treatmentis desired, the conductive coating may be formulated with an anionicdispersing agent. The combination of the cationic water-soluble polymerand the anionic dispersing agent typically causes the dispersion to bedestroyed and the conductive coating to be largely immobilized on thesurface of the fabric, thus preventing excessive penetration of thecoating. An alternative approach may include utilizing an anionicwater-soluble polymer in combination with a cationic dispersing agent.After the conductive coating has been applied to the fabric, the fabricis generally dried, and then the pre-treatment polymer may be washedoff. Washing may be accomplished by any technique typically used inmanufacturing operations, such as by running the fabric through washboxes in a tenter frame, by scouring, and the like.

In addition to the pre-treatment process., penetration of the conductingagent into the fabric may be controlled and determined by theapplication technique used to apply the conductive coating onto thefabric and the chemistry and viscosity of the conductive coating. In thecase of screen printing, the pressure on the printing bar or squeegeecan be adjusted to either increase or decrease the penetration of theconductive coating onto the fabric. Generally, higher viscosity coatingformulations will also limit penetration. It may be desirable toincrease such penetration, for example, to improve the static chargebleed-through from the face to the back of the fabric. Alternatively, itmay be preferable to decrease penetration, for example, to reduce seethrough to the uncoated side of the fabric (for instance, when only oneside of the fabric is coated with the conductive coating).

In one aspect of the present invention, the process of the currentinvention requires no special equipment; standard textile equipment maybe employed. By way of example, a fabric, either previously dyed or leftundyed, is attached to a rotary screen printing machine. The desiredscreen is inserted on the machine, and then a conductive coating isadded to the machine. One or more squeegees in the screen force aconductive paste through the holes in the screen, thereby forming aprinted pattern of conductive coating on the fabric below. The fabrictypically moves in a continuous fashion to a drying oven where theconductive coating is dried. Drying can be accomplished by any techniquetypically used in manufacturing operations, such as dry heat from atenter frame, microwave energy, infrared heating, steam, superheatedsteam, autoclaving, or the like, or any combination thereof. Typically,the fabric may be dried and/or cured for between about 30 seconds andabout 5 minutes at a temperature of between about 250 and about 375degrees F. Drying typically removes the water or solvent from the binderformulation in the conductive coating. The amount of conductive coatingrequired depends generally on the pattern chosen for the fabric, andthis is typically determined by the fabric's end-use. It may bepreferable that the coating coverage be between about 1% and about 50%,or even more preferably, perhaps between about 5% and about 30% asshown, for example, in FIGS. 1 through 3. The drying temperatures mayvary depending on the exact chemistry and/or viscosity of the conductivecoating employed in the application process. It is also contemplatedthat both sides of the fabric may be coated according to the method ofthe current invention either by simultaneously or successively coatingboth sides of the fabric.

After applying the electrically conductive coating to the fabric, thestatic dissipative textile may be tested for surface resistance using aresistivity meter. The static dissipative textile of the presentinvention may have a surface resistance in a range from about 10² toabout 10¹² ohms. The textile may more preferably have a surfaceresistance in a range from about 10⁴ to about 10¹⁰ ohms, and even morepreferably from about 10⁶ to about 10⁸ ohms. Typically, the lines of thepattern have a resistance of between about 10⁶ and about 10¹³ ohms perinch, or more preferably between about 10⁶ and about 10¹⁰ ohms per inch.

Following the coating process, the fabric may be further treated withone or more mechanical or chemical finishes. For example, depending onthe performance characteristics desired in the end-use of the staticdissipative textile, it may be desirable to add one or more chemicalssuch as flame resistance agents, soil release agents, pilling resistanceagents, strength enhancing agents, and the like, or combinationsthereof. Chemical application may be accomplished by immersion coating,padding, spraying, foam coating, or by any other technique whereby onecan apply a controlled amount of a liquid suspension to a fabric.Employing one or more of these application techniques may allow thechemical to be applied to the fabric in a uniform manner.

The static dissipative textile may further comprise at least one layerof a second fabric disposed adjacent to the electrically conductivecoating. The second fabric may be woven, knitted, or nonwoven fabric.Alternatively, the static dissipative textile may further comprise atleast one layer of foam material disposed adjacent to the electricallyconductive coating. The foam material may be polyurethane, polystyrene,polyether, polyester, silicone, acrylic, olefin, or the like, andcombinations thereof. Either of the alternative composite materials mayfurther include one or more additional layers of woven, knitted, ornonwoven fabric; one or more layers of film; one or more layers ofadhesive; or combinations thereof. The various layers of the compositematerial may be held together with adhesive or secured together by heator flame lamination and the like. The composite material may be used,for example, in automobile interiors, such as in automotive upholstery,wherein the upholstery fabric is typically adhered to a polyurethanefoam backing through the use of an adhesive or possibly with heatlamination. The composite material may be applicable for use in otherareas such as, for example, in residential or commercial upholstery orin carpeting.

The following examples illustrate various embodiments of the presentinvention but are not intended to restrict the scope thereof.

Static Test:

The relative propensity for a fabric to generate static build-up wastested using a device developed at Milliken & Company in Spartanburg,S.C. The test is currently used to certify the anti-static performanceof automotive seating and is further described in the proceedings of the2002 EOS/ESD Symposium, available from the ESD Association, 7900 TurinRoad, Building 3, Suite 2, Rome, N.Y. A schematic drawing of the testingmachine is shown in FIG. 8 and FIG. 9. FIG. 8 shows the testing device10 supported by stand 22. The testing device 10 used a pressurized aircylinder 18 to pull a carriage 20 across the face of a 3×9 inch piece offabric 12 in a controlled environment where the temperature was about 72degrees F. and the relative humidity was about 12%. Apolytetrafluoroethylene (PTFE) block 14 having about a 1.5 square inchface was positioned inside the carriage 20. A 1.6-kg weight 16 wasplaced on top of the PTFE block 14. The PTFE block 14 was dragged acrossthe surface of the fabric 12 as the carriage 20 was pulled by thepressurized air cylinder 18. FIG. 9 shows the PTFE block 14 was thendropped into a Faraday cup 24, which was connected by wire 26 to acharge meter 28. The net charge was measured with a Model 284Nanocoulomb Meter from Monroe Electronics of Lyndonville, N.Y. Thischarge was equal to the static build-up on the fabric 12. The test wasdesigned to mimic the actions of a person sliding in and out of a car.It provided an automated, statistically reproducible method forquantifying the static performance of fabrics and other flat materials.

Bounce Test:

The fabric's ability to withstand stress was tested using a cyclicimpact tester developed by Milliken & Company in Spartanburg, S.C. A75-pound weight was dropped 100,000 times from a height of about 2inches above the surface of the static dissipative fabric at a rate of20 drops, or cycles, per minute. The contact area of the bottom of theweight was a circle having about a ten-inch diameter. The number ofcycles were counted and stored electronically.

EXAMPLE 1

A 100% polyester double needle bar knit fabric which had been previouslyjet dyed, was screen printed with an electrically conductive coating inthe form of a paste in a diagonal grid pattern as shown in FIG. 3. Theconductive coating was made by mixing together 1314 grams of Timrex® SFG15 graphite which has an aspect ratio of 4 (available from Timcal Ltd.),79 grams of Synlube® 6277A (available from Milliken Chemical), and 12pounds of water until the graphite was dispersed. To this mix, 14.88pounds of an acrylic latex emulsion, T-91 (available from Noveon), wasadded. The mix was then thickened to a viscosity of 5000 Cps using anacrylic thickener, WTI Concentrate (available from ABCO Industries,Incorporated).

The conductive coating was screen printed on the back of the fabric in adiagonal grid pattern, as shown in FIG. 3, at a magnet pressure of 4with a 12 pound bar on a Stork rotary screen printing machine at a speedof 15 yards per minute. The fabric was then dried for 1 minute in a beltdrier at 310 degrees F. The resulting static dissipative fabric wastested using the Static Test described above. The surface resistance ofthe printed fabric was 10⁶ ohms. The fabric was also tested forFlammability (FMVSS 302) and achieved a SENBR rating. In addition, thepresence of the conducting grid on the back of the fabric was found tohave no adverse effect on fogging, seam slippage, lightfastness, hand,or appearance of the fabric. Submitting the sample to crumple,flex-fold, and stretch testing challenged the durability of theconductivity of the grid. These tests are well known to those skilled inthe art of testing automotive fabrics. The fabric showed no significantor permanent loss of conductivity. It is known to those skilled in theart that many of the tests used for automotive standards are typicallymore stringent than requirements for other fabric end-uses. Thus, theprinted fabric would likely be ideally suited for use as automotiveupholstery fabric; residential or commercial upholstery; cleanroomgarments, wipes, and mops; napery; and apparel.

EXAMPLE 2

Grid line spacing has been considered in relation to triboelectric, orstatic, charge. The fabric and process parameters as described inExample 1 were used to create four diagonal grid patterns having gridline spacing from 1.6 inches to 0.5 inches. A solid film of theconductive coating was also printed on the fabric. The resulting staticdissipative fabrics were tested using the Static Test described above.The Static Test showed that as the grid lines were printed closertogether, the triboelectric charge of the fabric decreased. Thisresulted in the creation of fabrics having increasingly higher staticdissipative properties as the grid lines were printed closer together.The results are shown in FIG. 6 and Table 1.

Accordingly, it may be preferable to apply the electrically conductivecoating to the fabric with line spacing in a range from about 0.2 toabout 10 inches. It may be more preferable to apply the electricallyconductive coating to the fabric with line spacing in a range from about0.5 to about 2 inches.

EXAMPLE 3

Line width has also been considered in relation to triboelectric, orstatic, charge. The fabric and process parameters as described inExample 2 were used except that the fabric was printed with twodifferent line widths, 1 millimeter (0.0394 inches) and 2 millimeters(0.0788 inches). The resulting static dissipative fabrics were testedusing the Static Test described above. The Static Test showed generallythat line width has little bearing on charge dissipation provided theline width is sufficient to obtain measurable conductivity. The resultsare shown in FIG. 6 and Table 1. Line width sufficient to obtainmeasurable conductivity may preferably be in a range from about 0.01 toabout 0.5 inches. Line width to obtain measurable conductivity may morepreferably be in a range from about 0.03 to about 0.2 inches.

TABLE 1 Effect of Grid Line Spacing and Line Width on Static PerformanceLine Width Triboelectric Line Spacing (inches) (millimeters) Charge (nC)Control (no treatment) 50.5 1.6 1 32 2 31 1.4 1 27 2 27.5 1.0 1 22 221.3 0.5 1 18 2 17.6 0 (solid film) 14

EXAMPLE 4

The fabric as described in Example 1 was prepared using two differentbinding agents. One fabric was prepared with T-91 acrylic latex(available from Noveon) and a second one was prepared with Sancure 861urethane (also available from Noveon). Both electrically conductivecoatings were made with a 28% weight loading (15 volume percent) ofTimcal® SFG 15 graphite (weight loading is calculated by dividing theweight of graphite by the weight of the total solids). Both fabrics werescreen printed with a diagonal grid pattern as shown in FIG. 3. Theseprinted fabrics were tested for durability using the Bounce Testdescribed above. The results are shown in FIG. 7 and Table 2. (“Before”represents the triboelectric charge on the fabric before the BounceTest, and “After” represents the triboelectric charge on the fabricafter the Bounce Test.) The charge was measured using the Static Testdescribed above. The surface resistance was measured using a Model 385Resistivity Meter from ACL, Inc. of Elk Grove, Ill. The fabrics wereable to withstand the force of a 75-pound weight dropped 100,000 timeson the fabrics without decreasing the effectiveness of the fabrics'ability to dissipate static electricity. This test emphasized thedurability of the electrically conductive pattern screen printed on thesurface of the fabrics.

TABLE 2 Durability of Fabric to Bounce Test Surface resistanceTriboelectric Line Spacing (inches) (ohms) Charge (nC) Control (notreatment)  >10¹²   40 Acrylic Before 10⁷ 28 After 10⁷ 28 UrethaneBefore 10⁷ 29 After 10⁷ 27

The above description and examples disclose the inventive staticdissipative textile having an electrically conductive surface whereinthe static dissipative textile typically comprises a fabric. Theelectrically conductive surface is generally comprised of a pattern oflines which provides relatively permanent static dissipation propertiesand conducts electric charge at virtually any humidity, while theelectrically conductive surface does not detrimentally affect theoverall appearance or tactile properties of the fabric. The electricallyconductive surface may be achieved by screen printing the fabric with anelectrically conductive coating comprised of a conducting agent and abinding agent, and optionally a dispersing agent and/or a thickeningagent. The fabric may be ideal for incorporation into articles ofautomotive upholstery; commercial and residential upholstery; cleanroomgarments, wipes, and other cleanroom accessories such as mops; napery;apparel; and any other article wherein it is desirable to manufacture astatic dissipative fabric having an electrically conductive surface.

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the scope of the invention described in the appended claims.

1. A method for providing a static dissipative textile comprising afabric having an electrically conductive surface, the method comprisingthe steps of: (a) providing a knitted, woven, or nonwoven fabric havinga first surface; (b) applying a water-soluble polymer to the firstsurface of the fabric, the water soluble-polymer having an ionic chargeselected from the group consisting of a cationic charge and an anioniccharge; (c) applying an electrically conductive coating composition tothe first surface of the fabric in a pattern comprised of a plurality oflines, the coating composition comprising a conducting agent a bindingagent, and a dispersing agent, the dispersing agent having an ioniccharge opposite the ionic charge of the water-soluble polymer; and (d)drying the fabric to provide a static dissipative textile having anelectrically conductive surface.
 2. The method of claim 1, wherein thelines have a line width of between about 0.01 and about 0.5 inches,wherein the electrically conductive coating is comprised of a conductingagent and a binding agent, and wherein the conducting agent has anaspect ratio equal to or greater than about
 2. 3. The method of claim 1,wherein the lines have a line width of between about 0.03 and about 0.2inches.
 4. The method of claim 1, wherein the step of drying the staticdissipative textile includes drying the static dissipative textile forbetween about 30 seconds and about 5 minutes at a temperature of betweenabout 250 and about 375 degrees F.
 5. The method of claim 1, furtherincluding the step of curing the static dissipative textile after thestep of drying the static dissipative textile.
 6. The method of claim 1,further including the step of exposing the static dissipative textile toone or more chemical or mechanical finishing processes after the step ofdrying the static dissipative textile.
 7. The method of claim 1, whereinthe electrically conductive coating is applied to the first surface ofthe fabric by screen printing, transfer printing, lithographic printing,ink jet printing, digital printing, or combinations thereof.
 8. Themethod of claim 6, wherein the electrically conductive coating isapplied to the first surface of the fabric by screen printing.
 9. Themethod of claim 1, wherein the pattern of the electrically conductivecoating forms at least one intersection of the lines.
 10. The method ofclaim 1, wherein the pattern of the electrically conductive coatingforms a plurality of intersections of the lines.
 11. The method of claim9, wherein the pattern of the electrically conductive coating formsconnected letters.
 12. The method of claim 1, wherein the binding agentof the electrically conductive coating comprises a material selectedfrom the group consisting of water-borne latexes, solvent-borne polymersystems, liquid rubbers, thermoplastic hot melts, thermoset hot melts,multi-component reactive polymers, and combinations thereof.
 13. Themethod of claim 12, wherein the binding agent of the electricallyconductive coating comprises a material selected from the groupconsisting of acrylic latex, polyurethane, silicone, polyvinyl chloridelatex, and combinations thereof.
 14. The method of claim 12, wherein thebinding agent has an elongation at break equal to or greater than about80 percent of the static dissipative textile's elongation at break,wherein the static dissipative textile's elongation at break iscalculated in the direction having the lowest elongation at break. 15.The method of claim 1, wherein the electrically conductive coatingfurther comprises a flame retardant compound.